function doOperation(op) {

    var t = op.toString()
    if(lineEdit1.focus)
        lineEdit1.text = t
    else  if(lineEdit2.focus)
        lineEdit2.text = t
    else  if(lineEdit3.focus)
        lineEdit3.text = t
    else  if(lineEdit4.focus)
        lineEdit4.text = t
    else  if(lineEdit5.focus)
        lineEdit5.text = t
    else  if(lineEdit6.focus)
        lineEdit6.text = t
}
